1. Field of the Invention
This invention relates to rotors of axial-flow machines, such as axial-flow compressors, axial-flow turbines, etc., and more particularly it is concerned with an axial-flow machine of the type having rotor blades assembled and disassembled axially on its rotor, wherein a removable spacer is mounted between the rotor blade mounting portions of the rotor to enable each rotor blade to be replaced with a new one as desired without requiring disassembling of the rotor.
2. Description of the Prior Art
In a stacked rotor type of axial-flow machine the discs of the rotor each have a recess on an inner side thereof, with the disc being stacked one over another in a suitable number of stages to meet the fluid performance and clamped together by stacking-bolts into a unitary structure. In the stacked-rotor type axial-flow machine, the rotor blades can be axially mounted and removed without disassembling the rotor by arranging the discs and the rotor blades in such a manner that the spacing interval between the discs is about twice as large as a length of a dovetail for receiving each rotor blade and a clearance of a size equal to the length of the dovetail is formed between the discs to thereby provide a removal allowance for the rotor blade. This allowance enables each rotor blade to be mounted and removed axially when desired. A rotor construction in which the rotor blades are mounted axially has high radial restraining strength and is suitable for use with an axial-flow machine in which high centrifugal forces are exerted on the rotor blades, because each rotor blade is individually mounted, as compared with a rotor construction in which the rotor blades are peripherally mounted. Also, the rotor of this construction has high damping effect with respect to the vibration of the rotor blades because the rotor blades do not restrain one another.
In an axial-flow machine, fluid performance is greatly affected by the size of a clearance between the ends of the rotor blades and the casing and the size of a clearance between the ends of stator blades and the surface of the rotor. The smaller these clearances, the higher the efficiency of the axial-flow machine.
Previously, in order to reduce the clearance between the ends of the stator blades and the surface of the rotor, an attempt has been made to form an extension of the dovetail section of each disc for mounting a rotor blade axially both to the forward and rearward stage sides so as to provide a channel on the surface of the rotor juxtaposed against the stator blades. This construction has, however, the disadvantage that, since the flanges overhang axially, the flanges undergo great deformation when exposed to centrifugal forces as the rotor rotates. This makes it necessary to provide a clearance between the stator blades and the flanges which is large enough to accommodate the deformation. This clearance is unable to have its size reduced. Also, deformation of the flanges, due to centrifugal forces, causes the surface (channel) of the rotor to become irregular, so that the flow of fluid moving therealong is disturbed and efficiency of the axial-flow machine is reduced. The above-noted construction is unable to provide an allowance for a rotor blade removing, thereby making it impossible to axially mount and remove the rotor blade without disassembling the rotor.
In another type of rotor of an axial-fow machine, a plurality of stator blades are assembled to the inner peripheral surface of the casing, with the ends of the stator blades being connected together by a shroud which is formed at its outer peripheral surface with a channel and at its inner peripheral surface with a labyrinth to keep the handled fluid from leaking from the rearward stage to the forward stage. In this type of rotor, it is possible to mount and remove each single rotor blade without disassembling the rotor by increasing the width of the shroud over and above the axial length of the dovetail. However, since leaks of the handled fluid from the rearward stage to the forward stage are only reduced in amount by a labyrinth, the fluid leaks from the rearward stage to the forward stage and blows out onto the rotor surface, thereby bending the flow of a portion of the fluid in the channel that is near the rotor surface and causing a reduction in efficiency.
In still another type of rotor construction disclosed, for example, in Japanese Laid Open Patent Application No. 8805/74, a spacer is mounted between the mounting portions of the adjacent rotor blades and the spacers are bolted to the rotor. By virtue of this arrangement, it is possible to mount and remove each single rotor blade without disassembling the rotor in this construction. However, a disadvantage of this construction resides in the fact that it is low in reliability because the spacers exposed to centrifugal forces are only bolted to the rotor. Moreover, the spacers themselves tend to undergo radial deformation at their axial opposite ends due to exposure to centrifugal forces, thereby adversely affecting the fluid efficiency.